Neonatal Heat Transfer, Routes of Heat Loss and Heat Gain

Abstract

Metabolic processes produce heat which is principally distributed in the body by the circulation of the blood but also in part by tissue conduction (for review, see 1). To maintain a constant body temperature the heat production and exchange with the environment must balance. Heat produced by the fetus has to pass through the mother to be eliminated and the umbilical circulation is the major route of heat exchange [2]. Immediately after birth the human infant is exposed to a colder temperature than in utero and at the same time fluid evaporates from the skin, with a resulting loss of heat and a decrease in body temperature. This is partly a physiological response as the body temperature at birth is higher than that in subsequent life. Exposure to cold may give rise to thermogenic responses which will increase basal heat production [3, 4, 5, 6, 7], and the skin circulation may decrease to reduce the heat loss [8]. Undue heat loss in an infant early after birth is usually prevented by wiping and covering the infant’s skin. Seriously ill term infants and preterm infants are nursed in an environment in which a normal body temperature can be maintained, either in an incubator at an ambient temperature within the thermoneutral zone, or under a radiant heater.